Aminonitrile production

ABSTRACT

Provided is a selective hydrogenation process for producing aminonitriles by contacting the corresponding dinitriles with a hydrogen-containing fluid in the presence of a hydrogenation catalyst, a solvent and a quaternary ammonium cyanate additive.

BACKGROUND OF INVENTION Field of the Invention.

The invention relates to a selective hydrogenation process for producingaminonitriles in the presence of a quaternary ammonium cyanate additive.

Aminonitriles are a class of important chemicals that have a variety ofindustrial applications. For example, aminonitriles can be used asmonomers for producing high molecular weight polyamides. Specifically,6-aminocapronitrile can be used to produce nylon 6.

Aminonitriles can be produced by catalytic partial hydrogenation ofdinitriles.

See, for example, U.S. Pat. No. 2,208,598, U.S. Pat. No. 2,257,814, U.S.Pat. No. 2,762,835, U.S. Pat. No. 3,322,815, U.S. Pat. No. 3,350,439,U.S. Pat. No. 3,591,618, U.S. Pat. No. 4,389,348, U.S. Pat. No.4,601,859, U.S. Pat. No. 5,151,543, U.S. Pat. No. 5,296,628, U.S. Pat.No. 5,512,697, U.S. Pat. No. 5,527,946, U.S. Pat. No. 5,986,127, U.S.Pat. No. 6,080,884, DE836938, DE848654, DE-A-19636768, JP-A-9040630 andWO00/64862, all of which are incorporated by reference herein for allpurposes as if fully set forth. However, the yield of and selectivity toa desired aminonitrile using some of the known processes may not be ashigh as desired, and the amount of the complete hydrogenation product(diamine) is also generally higher than desired.

U.S. Pat. No. 5,986,127 and WO00/64862 mentioned above describe the useof certain additives in the partial hydrogenation process to improve theyield of and/or selectivity to the desired aminonitrile product, and/orreduce the amount of fully hydrogenated product (diamine) produced.

We have now found new classes of compounds that also effectivelyfunction as improved yield and/or selectivity additives in the partialhydrogenation processes such as, for example, those mentioned inpreviously incorporated references.

SUMMARY OF INVENTION

In accordance with one aspect of the present invention, there isprovided a process for the partial hydrogenation of a dinitrile to anaminonitrile, comprising the step of contacting the dinitrile with ahydrogen-containing fluid in the presence of (a) a solvent comprisingliquid ammonia, an alcohol, or both; (b) a hydrogenation catalyst; and(c) an additive comprising a quaternary ammonium cyanate compound.

In accordance with another aspect of the present invention, there isprovided an improved process for preparing an aminonitrile from acorresponding dinitrile by contacting the dinitrile with ahydrogen-containing fluid in the presence of a solvent and ahydrogenation catalyst, wherein the improvement comprises contacting thedinitrile, hydrogen-containing fluid, solvent and hydrogenation catalystin the further presence of an additive comprising a quaternary ammoniumcyanate compound.

Another aspect of the present invention relates to a method forimproving the yield of and/or selectivity to an aminonitrile obtained bypartially hydrogenating a corresponding dinitrile with ahydrogen-containing fluid in the presence of a solvent and ahydrogenation catalyst, comprising the step of partially hydrogenatingthe dinitrile in the further presence of an effective amount of anadditive comprising a quaternary ammonium cyanate compound.

In yet another aspect of the present invention, there is provided acatalyst composition comprising a combination of (1) a hydrogenationcatalyst suitable for hydrogenating a dinitrile to an aminonitrile; and(2) an additive comprising a quaternary ammonium cyanate compound.

An advantage of this invention is that an aminonitrile can be producedin higher yield and/or having a higher selectivity to the aminonitrilewith the additive than without.

These and other features and advantages of the present invention will bemore readily understood by those of ordinary skill in the art from areading of the following detailed description. It is to be appreciatedthat certain features of the invention which are, for clarity, describedbelow in the context of separate embodiments, may also be provided incombination in a single embodiment. Conversely, various features of theinvention which are, for brevity, described in the context of a singleembodiment, may also be provided separately or in any subcombination.

DETAILED DESCRIPTION

According to this invention, a dinitrile is contacted with ahydrogen-containing fluid in the presence of a solvent, a catalyst and aquaternary ammonium cyanate compound.

Suitable dinitriles for use herein have the general formula R(CN)₂,wherein R is a hydrocarbylene group selected from the group consistingof an alkylene, arylene, alkenylene, alkarylene and aralkylene group.One dinitrile or combinations of different dinitriles may be used.Preferred hydrocarbylene groups contain from 2 to 25, more preferably 2to 15, and most preferably 2 to 10 carbon atoms per group. In otherwords, preferred dinitriles contain from 4 to 27, more preferably 4 toabout 17, and most preferably 4 to 12, carbon atoms per dinitrilemolecule. The preferred type of hydrocarbylene group is an alkylenegroup.

Examples of suitable dinitriles include, but are not limited to,adiponitrile; methylglutaronitrile; alpha,omega-pentanedinitrile;alpha,omega-heptanedinitrile; alpha,omega-nonanedinitrile;alpha,omega-dodecanedinitrile; alpha,omega-pentadecanedinitrile;alpha,omega-icosanedinitrile; alpha,omega-tetracosane-dinitrile;3-methylhexanedinitrile; 2-methyl-4-methylene-octanedinitrile; andcombinations of two or more thereof.

Preferably the carbon atoms of the starting dinitrile are arranged in abranched or linear chain. Preferred examples are adiponitrile(hydrogenated to 6-aminocapronitrile), methylglutaronitrile(hydrogenated to two isomeric aminonitriles:5-amino-2-methylvaleronitrile and 5-amino-4-methyl-valeronitrile) andalpha,omega-dodecanedinitrile (hydrogenated to the correspondingaminonitrile). The preferred dinitrile is adiponitrile because itsselective hydrogenation product, 6-aminocapronitrile, is a well-knownmonomer for polymerization applications.

Any hydrogen-containing fluid can be used in the invention as long asthere is sufficient hydrogen in the fluid to selectively hydrogenate adinitrile to an aminonitrile. The term fluid refers to liquid, gas orboth. The hydrogen content in the fluid can range from 1 to 100%,preferably about 50 to about 100%, and most preferably 90 to 100% byvolume. The presently preferred hydrogen-containing fluid issubstantially pure hydrogen gas.

The molar ratio of hydrogen (in the hydrogen-containing fluid) todinitrile is not critical as long as sufficient hydrogen is present toproduce the desired aminonitrile. Hydrogen is generally used in excess.Hydrogen pressures are generally in the range of about 50 to about 2000psig (about 0.45 to about 13.89 MPa), with from about 200 to about 1000psig (about 1.48 to about 7.00 MPa) preferred.

Any solvent that comprises either liquid ammonia or an alcohol can beused in the invention. The concentration of liquid ammonia in thesolvent can range from about 20 to about 100%, preferably about 50 toabout 100%, and most preferably about 80% to about 100%, by weight oftotal solvent. A substantially pure liquid ammonia is preferred.However, if an alcohol is also present in the solvent, the concentrationof ammonia can be adjusted based on the quantity of alcohol used, whichis discussed in further detail below. The molar ratio of ammonia todinitrile is preferably about 1:1 or greater, and is generally in therange of from about 1:1 to about 30:1, more preferably from about 2:1 toabout 20:1.

Any alcohol that can facilitate the selected hydrogenation of adinitrile to an aminonitrile can be used in this invention. Preferredare alcohols with 1 to 10, more preferably 1 to 4, carbon atoms permolecule. Examples of suitable alcohols include, but are not limited to,methanol, ethanol, propanol, isopropyl alcohol, butanol, isobutylalcohol, pentanol, hexanol, heptanol, octanol, nonanol, decanol, andcombinations of two or more thereof. The most preferred alcohol (whenused) is methanol. The alcohol can generally be present in the solventin the concentration of from about 20 to about 100%, preferably about 30to about 99%, by weight based on the total solvent weight.

Typically when an alcohol is use, the solvent further comprises a basethat is substantially soluble in the solvent. The term substantiallyrefers to more than trivial. Preferred bases are ammonia, an ammoniumbase or an inorganic base such as, for example, alkali metal oxides,alkaline earth metal oxides, alkali metal hydroxides, alkaline earthmetal hydroxides, partially neutralized acids in which one or moreprotons of the acids are replaced with ammonium ion, alkali metal ions,alkaline earth metal ions, or combinations of two or more thereof.Specific examples of suitable bases include, but are not limited toammonia, lithium hydroxide, sodium hydroxide, potassium hydroxide,sodium bicarbonate, sodium carbonate, potassium bicarbonate, orcombinations of two or more thereof. The most preferred bases areammonia, lithium hydroxide and sodium hydroxide for they are readilyavailable and inexpensive.

A base can be present in the solvent in any quantity so long as thequantity can facilitate the selective hydrogenation of a dinitrile to anaminonitrile. Generally, a base can be present in the solvent in therange of from about 0.1 to about 10 weight %, based on the total weightof the starting dinitrile.

The catalyst in the process is a hydrogenation catalyst suitable forhydrogenating a dinitrile to an aminonitrile. Preferred are catalystsbased on transition metals selected from the group consisting of iron,cobalt, nickel, rhodium and combinations thereof. The catalyst may alsocontain one or more promoters in addition to the transition metalsmentioned above, for example, one or more of Group VIB and Group VIImetals such as chromium, molybdenum and tungsten. The catalyst can alsobe in the form of an alloy, including a solid solution of two or moremetals, or an individual metal.

The catalytic metal can also be supported on an inorganic support suchas alumina, magnesium oxide and combinations thereof. The metal can besupported on an inorganic support by any means known to one skilled inthe art such as, for example, impregnation, coprecipitation, ionexchange, and combinations of two or more thereof. The preferredinorganic support is magnesium oxide, and the preferred supportedcatalyst is a magnesium oxide supported nickel-iron catalyst.

The catalyst can be present in any appropriate physical shape or form.It can be in fluidizable forms, extrudates, tablets, spheres orcombinations of two or more thereof. The catalyst may be in sponge metalform, for example, the Raney® nickels and Raney® cobalts. The molarratio of catalyst to dinitrile can be any ratio as long as the ratio cancatalyze the selective hydrogenation of a dinitrile. The weight ratio ofcatalyst to dinitrile is generally in the range of from about 0.0001:1to about 1:1, preferably about 0.001:1 to about 0.5:1. If the catalyticmetal is supported on an inorganic support or is a portion of alloy orsolid solution, the catalytic metal is generally present in the range offrom about 0.1 to about 60, preferably about 1 to about 50, and mostpreferably about 2 to about 50 weight %, based on the total catalystweight.

The preferred catalyst is a sponge metal type catalyst. The metalliccomponent is iron, cobalt, nickel or combinations thereof. Commerciallyavailable catalysts of this type are promoted or unpromoted Raney® Ni orRaney® Co catalysts that can be obtained from the Grace Chemical Co.(Columbia, Md.), or alternative sponge metal catalysts available, forexample, from Activated Metals Corporation (Sevierville, Tenn.) orDegussa (Ridgefield Park, N.J.).

In the case of the preferred supported nickel/iron catalyst, the rate ofadiponitrile conversion increases with the amount of Ni deposited on thesupport. The preferred concentration of Ni is between about 5 and about50 weight %, and especially between about 25 and about 35 weight %,based on the catalyst weight (metals+support). The preferredconcentration of Fe is between about 0.2 and about 20 weight %, andespecially between about 0.5 and about 10 weight %, based on thecatalyst weight (metals+support).

Further details on the above components can be found from various of thepreviously incorporated references. Specific reference may be had, forexample, to U.S. Pat. No. 2,208,598, U.S. Pat. No. 2,257,814, U.S. Pat.No. 2,762,835, U.S. Pat. No. 3,322,815, U.S. Pat. No. 5,151,543, U.S.Pat. No. 5,296,628, U.S. Pat. No. 5,512,697, U.S. Pat. No. 5,527,946,U.S. Pat. No. 5,986,127, U.S. Pat. No. 6,080,884 and WO00/64862.

A wide variety of quaternary ammonium cyanate compoundshave been foundthat can effect the selectivity/yield improvement in the invention.

The term improvement is referred to as enhanced selectivity toaminonitrile product at conversions greater than about 70%, preferablyconversions greater than about 80%, and especially conversions greaterthan about 90%, as compared to the selectivity without the use of theadditive of this invention. An effective amount of the additive isamount required to achieve the aforementioned enhanced selectivityand/or an improved overall yield of aminonitrile, as compared to withoutthe use of the additive.

Examples of suitable quaternary ammonium cyanate compounds aretetraalkylammonium cyanate compounds and mixed tetraalkyl/arylammoniumcyanate compounds.

In preferred tetraalkylammonium cyanate embodiments, the alkyl groups ofthe tetraalkylammonium cyanate compounds each individually contain from1 to 8 carbon atoms, and more preferably 1-4 carbon atoms. It ispreferred that all four of the alkyl groups in a molecule are the same,but mixtures having different tetraalkyl substituents are suitable foruse herein. Examples of suitable tetraalkylammonium cyanate compoundsinclude, but are not limited to, tetramethylammonium cyanate,tetraethylammonium cyanate, tetrapropylammonium cyanate andtetrabutylammonium cyanate. As indicated above, combinations of two ormore tetraalkylammonium cyanate compounds are also suitable. In mixedtetraalkyl/arylammonium cyanate compounds, the alkyl groups are asdescribed above; the aryl groups may be phenyl, naphthyl oralkyl-substituted phenyl or naphthyl, with alkyl described as above.

The additive is present during the contacting in any quantity that canimprove the selective hydrogenation of a dinitrile to its correspondingaminonitrile (e.g., an effective amount). Generally, the weight ratio ofthe additive to the catalyst is in the range of from about 0.01:1 toabout 5:1, preferably about 0.05:1 to about 3:1, more preferably about0.1:1 to 2:1, and especially about 0.1:1 to about 1:1.

The catalyst and additive can be separately introduced into contact witha dinitrile; however, it is preferred that the catalyst, whether it isin its metal form or in an alloy or solid solution or on an inorganicsupport, is precontacted with the additive. This may be done in asolvent such as, for example, an alcohol, ether, ester, ammonia orcombinations of two or more thereof. Further preferably theprecontacting is also carried out in a hydrogen-containing fluid such asdescribed above. Contacting of the catalyst and additive produces apretreated catalyst. The pretreated catalyst can be washed with asolvent disclosed above, preferably under anaerobic condition to producean additive-treated catalyst.

The contacting of the catalyst and additive can be carried out under anyconditions effective to produce an additive-treated catalyst that canimprove selective hydrogenation of a dinitrile or the selectivity to anaminonitrile. Generally, the entire process for producing theadditive-treated catalyst can be carried out by contacting a catalystwith an additive disclosed above at a temperature in the range of fromabout 20° C. to about 150° C., preferably about 30° C. to about 100° C.,under the same general pressures as described above, for about 5 secondsto about 25 hours.

The partial hydrogenation process of the present invention can becarried out at a temperature in the range of from about 25 to about 150°C., preferably about 40 to about 100° C., most preferably about 60 toabout 80° C., at a total pressure generally in the range of about 50 toabout 2000 psig (about 0.45 to about 13.89 MPa), with from about 200 toabout 1000 psig (about 1.48 to about 7.00 MPa) preferred, for a timeperiod generally in the range of from about 15 minutes to about 25hours, preferably about 1 hour to about 10 hours.

The process of the invention can be operated batch wise or continuouslyin an appropriate reactor. Stirring or agitation of the reaction mixturecan be accomplished in a variety of ways known to those skilled in theart. The partial hydrogenation of the starting dinitrile to itscorresponding aminonitrile with high selectivity at high conversions ofthe dinitrile makes this process efficient and useful.

Further general and specific process details can be found from variousof the previously incorporated references. Specific reference may behad, for example, to U.S. Pat. No. 2,208,598, U.S. Pat. No. 2,257,814,U.S. Pat. No. 2,762,835, U.S. Pat. No. 3,322,815, U.S. Pat. No.5,151,543, U.S. Pat. No. 5,296,628, U.S. Pat. No. 5,512,697, U.S. Pat.No. 5,527,946, U.S. Pat. No. 5,986,127, U.S. Pat. No. 6,080,884 andWO00/64862.

The following examples further illustrate the process of the inventionand are not to be construed to unduly limit the scope of the invention.

The meaning of terms used in the Examples is defined as follows: Yieldof aminonitrile is the measured concentration of aminonitrile divided bythe starting concentration of dinitrile.

Conversion of the dinitrile is the difference between the starting andthe instant concentration of dinitrile, divided by the startingconcentration of dinitrile.

Selectivity to aminonitrile is the measured yield of aminonitriledivided by conversion of the dinitrile at that instance.

COMPARATIVE EXAMPLE 1

A sponge Ni catalyst (1.2 g) promoted with Fe and Cr (Activated Metals,A4000, without any further additives) was added to a 50 cc autoclavetogether with 3.2 g adiponitrile (ADN) and 35 cc of liquid ammonia toform a mixture. Hydrogen was introduced to the autoclave and the ADN washydrogenated at 60° C. under the total pressure of 1045 psig (7.31 MPa)at ca. 1500 rpm. Total conversion of ADN was reached within 30 minuteson stream. The maximum yield of aminocapronitrile was 57% at 90% ADNconversion for a selectivity of 63%.

COMPARATIVE EXAMPLE 2

To a 300 cc autoclave, was charged 7.7 g Raney® Co (obtained from W. R.Grace Co., catalog number 2724), 0.77 g water, 26 g ADN, and 139 gliquid ammonia. The content was hydrogenated at 70° C., under the totalpressure of 1000 psig (7.00 MPa) at 1000 rpm. Total conversion of ADNwas reached within 40 minutes on stream. The maximum yield ofaminocapronitrile was 58% at 90% ADN conversion for a selectivity of64%.

COMPARATIVE EXAMPLE 3

To a 50 cc autoclave, was charged 1.2 g of a 5% rhodium on aluminacatalyst (obtained from Engelhard), 3.2 g ADN, and 35 ml liquid ammonia.The content was hydrogenated at 80° C., under the total pressure of 1060psig (7.41 MPa), at 1500 rpm. Total conversion of AND was reached within30 minutes on stream. The maximum yield of aminocapronitrile was 41% at96% ADN conversion, with the major product being hexamethylene diamine.

EXAMPLE 1

1.2 g of sponge Ni catalyst (Degussa BLM 112W) was charged into a 50 ccautoclave, together with 0.25 g of tetraethylammonium cyanate, 1.2 g ofand 35 ml of liquid ammonia was added. The mixture was heated to 70° C.,and reacted with hydrogen at a total pressure of 1052 psig (7.00 MPa).After 25 minutes, the yield of 6-aminocapronitrile reached ca. 78% at88% AND conversion for a selectivity of 89%.

EXAMPLE 2

1.2 g of sponge Ni catalyst (Degussa BLM 112W) was charged into a 50 ccautoclave, together with 2.0 g of tetraethylammonium cyanate.Subsequently, 35 ml of liquid ammonia was added, and the mixture washeated to 70° C. with stirring. The pressure was adjusted to 1052 psig(7.00 MPa) with hydrogen, and the autoclave was kept under suchconditions for 1 hr. After cooling, the liquid phase was filtered off,leaving the pretreated catalyst inside of the autoclave. 1.2 g of ADNwas injected into the autoclave and 35 ml of liquid ammonia was added.The mixture was heated to 70° C., and reacted with hydrogen at a totalpressure of 1052 psig (7.00 MPa). After 60 minutes the yield of6-aminocapronitrile reached ca. 74% at 92% ADN conversion for aselectivity of 80%.

EXAMPLE 3

1.2 g of sponge Ni catalyst (Degussa BLM 112W) was charged into a 50 ccautoclave, together with 0.5 g of tetraethylammonium cyanate, 1.2 g ofand 35 ml of liquid ammonia was added. The mixture was heated to 70° C.,and reacted with hydrogen at a total pressure of 1052 psig (7.41 MPa).After 37 minutes, the yield of 6-aminocapronitrile reached ca. 76% at93% ADN conversion for a selectivity of 82%.

EXAMPLE 4

1.2 g of sponge Ni catalyst (Degussa BLM 112W) was charged into a 50 ccautoclave, together with 0.25 g of tetraethylammonium cyanate.Subsequently, 35 ml of liquid ammonia was added, and the mixture washeated to 80° C. with stirring. The pressure was adjusted to 1052 psig(7.00 MPa) with hydrogen, and the autoclave was kept under suchconditions for 1 hr. After cooling, the liquid phase was filtered off,leaving the pretreated catalyst inside of the autoclave. 1.2 g of ADNwas injected into the autoclave and 35 ml of liquid ammonia was added.The mixture was heated to 80° C., and reacted with hydrogen at a totalpressure of 1052 psig (7.41 MPa). After 12 minutes, the yield of6-aminocapronitrile reached ca. 75% at 88% ADN conversion for aselectivity of 85%.

EXAMPLE 5

1.2 g of sponge Ni catalyst (Degussa BLM 112W) was charged into a 50 ccautoclave, together with 0.25 g of tetraethylammonium cyanate.Subsequently, 35 ml of liquid ammonia was added, and the mixture washeated to 60° C. with stirring. The pressure was adjusted to 1052 psig(7.00 MPa) with hydrogen, and the autoclave was kept under suchconditions for 1 hr. After cooling, the liquid phase was filtered off,leaving the pretreated catalyst inside of the autoclave. 1.2 g of ADNwas injected into the autoclave and 35 ml of liquid ammonia was added.The mixture was heated to 60° C., and reacted with hydrogen at a totalpressure of 1052 psig (7.41 MPa). After 70 minutes, the yield of6-aminocapronitrile reached ca. 77% at 93% ADN conversion for aselectivity of 83%.

EXAMPLE 6

1.2 g of sponge Ni catalyst (Degussa BLM 112W) was charged into a 50 ccautoclave, together with 0.25 g of tetraethylammonium cyanate.Subsequently, 35 ml of liquid ammonia was added, and the mixture washeated to 80° C. with stirring. The pressure was adjusted to 1054 psig(7.00 MPa) with hydrogen, and the autoclave was kept under suchconditions for 1 hr. After cooling, the liquid phase was filtered off,leaving the pretreated catalyst inside of the autoclave. 1.2 g of ADNwas injected into the autoclave and 35 ml of liquid ammonia was added.The mixture was heated to 70° C., and reacted with hydrogen at a totalpressure of 1054 psig (7.41 MPa). After 65 minutes, the yield of6-aminocapronitrile reached ca. 77% at 95% ADN conversion for aselectivity of 81%.

EXAMPLE 7

1.2 g of sponge Ni catalyst (Degussa BLM 112W) was charged into a 50 ccautoclave, together with 0.5 g of tetraethylammonium cyanate.Subsequently, 35 ml of liquid ammonia was added, and the mixture washeated to 70° C. with stirring. The pressure was adjusted to 1052 psig(7.00 MPa) with hydrogen, and the autoclave was kept under suchconditions for 1 hr. After cooling, the liquid phase was filtered off,leaving the pretreated catalyst inside of the autoclave. 1.2 g of ADNwas injected into the autoclave and 35 ml of liquid ammonia was added.The mixture was heated to 70° C., and reacted with hydrogen at a totalpressure of 1054 psig (7.41 MPa). After 42 minutes, the yield of6-aminocapronitrile reached ca. 77% at 92% ADN conversion for aselectivity of 84%.

What is claimed is:
 1. A process for the partial hydrogenation of adinitrile to an aminonitrile, comprising the step of contacting thedinitrile with a hydrogen-containing fluid in the presence of (a) asolvent comprising liquid ammonia, an alcohol or both; (b) ahydrogenation catalyst; and (c) an effective amount of an additivecomprising a quaternary ammonium cyanate compound.
 2. The process ofclaim 1, wherein the dinitrile has the general formula R(CN)₂, wherein Ris an alkylene group containing from 2 to 25 carbon atoms.
 3. Theprocess of claim 1, wherein the dinitrile is selected from the groupconsisting of adiponitrile, methylglutaronitrile andalpha,omega-dodecanedinitrile.
 4. The process of claim 1, wherein thehydrogenation catalyst comprises a transition metal selected from thegroup consisting of iron, cobalt, nickel, rhodium and combinationsthereof.
 5. The process of claim 4, wherein the hydrogenation catalystis in sponge metal form.
 6. The process of claim 4, wherein thecatalytic metal is supported on an inorganic support.
 7. The process ofclaim 1, wherein the quaternary ammonium cyanate compound is atetraalkylammonium cyanate compound and the alkyl groups of thetetraalkylammonium cyanate compound each individually contains from 1 to8 carbon atoms.
 8. The process of claim 7, wherein thetetraalkylammonium cyanate compound is selected from the groupconsisting of tetramethylammonium cyanate, tetraethylammonium cyanate,tetrapropylammonium cyanate and tetrabutylammonium cyanate.
 9. Theprocess of claim 1, wherein the weight ratio of additive tohydrogenation catalyst is in the range of from about 0.01:1 to about5:1.
 10. The process of claim 1, wherein the dinitrile is selected fromthe group consisting of adiponitrile, methylglutaronitrile andalpha,omega-dodecanedinitrile; the hydrogenation catalyst comprises atransition metal selected from the group consisting of iron, cobalt,nickel, rhodium and combinations thereof; and the weight ratio ofadditive to hydrogenation catalyst is in the range of from about 0.01:1to about 5:1.
 11. The process of claim 7, wherein the dinitrile isselected from the group consisting of adiponitrile, methylglutaronitrileand alpha,omega-dodecanedinitrile; the hydrogenation catalyst comprisesa transition metal selected from the group consisting of iron, cobalt,nickel, rhodium and combinations thereof; and the weight ratio ofadditive to hydrogenation catalyst is in the range of from about 0.01:1to about 5:1.
 12. The process of claim 8, wherein the dinitrile isselected from the group consisting of adiponitrile, methylglutaronitrileand alpha,omega-dodecanedinitrile; the hydrogenation catalyst comprisesa transition metal selected from the group consisting of iron, cobalt,nickel, rhodium and combinations thereof; and the weight ratio ofadditive to hydrogenation catalyst is in the range of from about 0.01:1to about 5:1.
 13. An improved process for the preparing an aminonitrilefrom a corresponding dinitrile by contacting the dinitrile with ahydrogen-containing fluid in the presence of a solvent and ahydrogenation catalyst, wherein the improvement comprises contacting thedinitrile, hydrogen-containing fluid, solvent and hydrogenation catalystin the further presence of an effective amount of an additive comprisinga quaternary ammonium cyanate compound.
 14. The improved process ofclaim 13, wherein the quaternary ammonium cyanate compound is atetraalkylammonium cyanate compound and the alkyl groups of thetetraalkylammonium cyanate compound each individually contains from 1 to8 carbon atoms.
 15. The improved process of claim 14, wherein thetetraalkylammonium cyanate compound is selected from the groupconsisting of tetramethylammonium cyanate, tetraethylammonium cyanate,tetrapropylammonium cyanate and tetrabutylammonium cyanate.
 16. Theimproved process of claim 13, wherein the dinitrile is selected from thegroup consisting of adiponitrile, methylglutaronitrile andalpha,omega-dodecanedinitrile; the hydrogenation catalyst comprises atransition metal selected from the group consisting of iron, cobalt,nickel, rhodium and combinations thereof; and the weight ratio ofadditive to hydrogenation catalyst is in the range of from about 0.01:1to about 5:1.
 17. A method for improving the yield of and/or selectivityto an aminonitrile obtained by partially hydrogenating a correspondingdinitrile with a hydrogen-containing fluid in the presence of a solventand a hydrogenation catalyst, comprising the step of partiallyhydrogenating the dinitrile in the further presence of an effectiveamount of an additive comprising a quaternary ammonium cyanate compound.18. The method of claim 17, wherein the quaternary ammonium cyanatecompound is a tetraalkylammonium cyanate compound and the alkyl groupsof the tetraalkylammonium cyanate compound each individually containsfrom 1 to 8 carbon atoms.
 19. The method of claim 18, wherein thetetraalkylammonium cyanate compound is selected from the groupconsisting of tetramethylammonium cyanate, tetraethylammonium cyanate,tetrapropylammonium cyanate and tetrabutylammonium cyanate.
 20. Themethod of claim 17, wherein the dinitrile is selected from the groupconsisting of adiponitrile, methylglutaronitrile andalpha,omega-dodecanedinitrile; the hydrogenation catalyst comprises atransition metal selected from the group consisting of iron, cobalt,nickel, rhodium and combinations thereof; and the weight ratio ofadditive to hydrogenation catalyst is in the range of from about 0.01:1to about 5:1.